1. Field of the Invention
The present invention relates to a powder conveying apparatus conveying while agitating powder such as developer.
2. Description of the Background Art
Image forming apparatuses, such as copying machine, printer and facsimile, forming an image by using developer containing toner particles have a developing device for conveying powder such as developer containing toner while stirring it. Such a developing device has a powder agitating/conveying member conveying while agitating powder. The powder agitating/conveying member has a screw blade connected to a shaft that agitates and conveys the powder by revolution around an axis thereof.
For prevention of toner scattering and image defects such as high background soil by thorough agitation of the powder, known is a configuration having, between screw blades, a rib inclined toward revolution direction from an external surface to a center of the shaft and also inclined toward the direction almost perpendicular to the helical direction of the screw blade from the axial direction of the shaft (see, for example, Japanese Unexamined Patent Publication No. 2003-270947).
However, such a configuration containing a rib causes a problem that the powder conveying speed became lower than that when the rib is absent. In the recent trend toward acceleration of printing, there is a need for higher printing speed. Higher printing speed leads to higher consumption rate of the developer containing toner, which, in turn, demands higher conveying speed of the developer. On the other hand, the increase in conveying speed causes a problem of insufficient agitation of the developer.